Accelerating loss of seagrasses across the globe threatens coastal ecosystems

Abstract

Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 km 2 yr ؊1 since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% yr ؊1 before 1940 to 7% yr ؊1 since 1990. Seagrass loss rates are comparable to those reported for mangroves, coral reefs, and tropical rainforests and place seagrass meadows among the most threatened ecosystems on earth.ecosystem decline ͉ global trajectories ͉ habitat loss ͉ marine habitat

Recovery of marine animal populations and ecosystems

“…By contrast, no recovery occurred in the southern bays, owing to seed limitation, before active restoration efforts. This is one of a few examples where restoration of lost seagrass beds has been successful [6]. On many temperate coasts, kelp forests have recovered from deforestation by sea urchins after sea urchin populations were reduced by natural predators (e.g.…”

“…Awareness, legal protection and enforcement of management plans are also crucial. Learning from historical recovery successes and failures is essential for implementing realistic conservation goals and promising management strategies.A new focus on recovery An increasing number of studies have reported strong declines in marine animal populations and the degradation of ocean ecosystems over past decades and centuries around the world [1][2][3][4][5][6][7], leading to a widespread perception of empty oceans and polluted waters. Yet, throughout history, humans have responded to declining resource abundance and ecosystem degradation by implementing management and conservation measures.…”

“…However, despite long periods of intense human impacts, most marine species persist and some populations do show signs of recovery [3,8,9]. Similarly, many coastal habitats, including wetlands, seagrass beds, mangrove and kelp forests, and oyster and coral reefs, have been severely reduced or degraded [2][3][4]6], yet partial recovery has been achieved in some regions in response to protection and pollution controls [3,13]. Restoration attempts at an ecosystem level have often been followed by the return and recovery of former species assemblages and ecosystem functions [13][14][15][16][17], but some ecosystems have remained in an altered state [18].…”

Combined nutrient and macroalgae loads lead to response in seagrass indicator properties

“…Decline of seagrass meadows due to human activity has been reported in recent years throughout the world (Orth et al, 2006;Waycott et al, 2009). One of the most important threats to seagrasses is eutrophication, which could result from increased fertilizer use and marine cultivation (Burkholder et al, 2007;Orth et al, 2006).…”

Cover versus recovery: Contrasting responses of two indicators in seagrass beds

“…Despite their capacity to adapt and to cope to some extent with environmental changes, seagrasses suffer rapid and large-scale losses worldwide, their distribution is declining and their survival threatened (Orth et al, 2006). Anthropogenic influences, causing changes in soil chemistry, nutrient loading, hydrodynamics and sediment dynamics are responsible for the seagrass disappearance over the last 40 years (Orth et al, 2006 and references therein; Waycott et al, 2009). …”